Pressure-sensitive record sheet and method of making

ABSTRACT

THERE IS PROVIDED BY THIS INVENTION A MINUTE, MULTIPLEDROPLET-RETAINING PRESSURE-RUPTURABLE CAPSULE UNIT FOR SUPPLYING MARKING LIQUID, THE USE OF WHICH IN A PAPER COATING CONSTITUTES A NEW METHOD OF AIDING IN THE PROTECTION OF MINUTE CAPSULES AGAINST ACCIDENTAL RUPTURE AND LOSS OF MARKING LIQUID UNTIL MARKING PRESSURES ARE APPLIED. THE CAPSULE UNIT COMPRISES A BOUNDING AND RETAINING MATRIX OF DEPOSITED POLYMER FILM MATERIAL IN WHICH THE DROPLETS ARE RETAINED IN RANDOM DISTRIBUTION, THE DROPLETS BEING OF TWO KINDS, DIFFERING IN SIZE AND MATERIAL. THE DROPLETS OF SMALLER SIZE ARE OF CONCENTRATED LIQUID MARKING MATERIAL, WHEREAS THE LARGER DROPLETS ARE OF A DILUENT FOR THE LIQUID OF THE SMALLER CAPSULES, SO, THAT, WHEN A CAPSULE IS SMASHED IN ITS ENTIRETY, IT RELEASES A LOW-VISCOSITY DILUTED MARKING LIQUID THAT QUICKLY DRIES ON PAPER BY EVAPORATION AND BY IMBIBITION. THE LARGER RETAINED DROPLETS PROTRUDE AND CAUSE BUMPS IN THE DEPOSITED MATRIX. WHEN THE UNITS ARE USED AS A COATING ON RECORD SHEET MATERIAL IN CLOSE JUXTAPOSITION, AS DRIED FROM AN APPLIED LIQ-   UID COATING SLURRY OF THE UNITS, THE PROTUBERANCES OF THE LARGE DROPLETS PROTECT THE SMALLER DROPLETS FROM ACCIDENTAL PRESSURE-RELEASE BY SCUFFING TYPES OF CASUALLY-APPLIED HANDLING FORCES. THUS A SHEET OF PAPER SENSITIZED TO DIRECT PRINTING PRESSURE WITH A COATING OF THESE CAPSULE UNITS FOR USE AS PART OF A RECORD UNIT SYSTEM SHOWS BOTH EXCELLENT MARKING-LIQUID TRANSFER EFFICIENCY AND ACCIDENTAL-SMUDGE RESISTANCE-A MARKED IMPROVEMENT OVER PRESENT COMMERCIAL PAPERS COATED WITH CAPSULAR AGGREGATES HAVING DROPLETS OF UNIFORM SIZE AND COMPOSITION.

June 12, 1973 B. w. BROCKETT ET AL 3,738,857

PRESSURE-SENSITIVE RECORD SHEET AND METHOD OF MAKING Original Filed Nov. 8. 1968 MINUTE ENCAPSULATED DROPLET OF AN INERT MINUTE ENCAPSULATED DROPLET OF A LIQUID DISPERSION OF A DYE CAPSULE WALL MATERIAL CAPSULE UNITI ENCAPSULATED AGGREGATION OF DROPLETS FIG.2

mvemoas CA UNIT BRUCE w. BROCKETT FREDRICK D.WEAVER PAPER 1 3 THEIR ATTORNEY United States Patent O US. Cl. 11736.1 2 Claims ABSTRACT OF THE DISCLOSURE There is provided by this invention a minute, multipledroplet-retaining pressure-rupturable capsule unit for supplying marking liquid, the use of which in a paper coating constitutes a new method of aiding in the protection of minute capsules against accidental rupture and loss of marking liquid until marking pressures are applied. The capsule unit comprises a bounding and retaining matrix of deposited polymer film material in which the droplets are retained in random distribution, the droplets being of two kinds, diifering in size and material. The droplets of smaller size are of concentrated liquid marking material, whereas the larger droplets are of a diluent for the liquid of the smaller capsules, so, that, when a capsule is smashed in its entirety, it releases a low-viscosity diluted marking liquid that quickly dries on paper by evaporation and by imbibition. The larger retained droplets protrude and cause bumps in the deposited matrix. When the units are used as a coating on record sheet material in close juxtaposition, as dried from an applied 1iq uid coating slurry of the units, the protuberances of the 3 large droplets protect the smaller droplets from accidental pressure-release by scufling types of casually-applied handling forces. Thus a sheet of paper sensitized to direct printing presure with a coating of these capsule units for use as part of a record unit system shows both excellent marking-liquid transfer efficiency and accidental-smudge resistance-a marked improvement over present commercial papers coated with capsular aggregates having droplets of uniform size and composition.

This is a division of application Ser. No. 774,312, filed Nov. 8, 1968.

OBJECT OF THE INVENTION The art of making multiple-sheet, pressure-sensitive, record units, such as NCR paper, is well known. In one such record unit system, a colorless chromogenic liquid is released by writing or typing pressures from minute enclosing capsules in a coating on one sheet of paper and transferred to another sheet of paper, where its color is developed by a co-reactant to produce a distinctively colored mark. To prevent undesired rupture of the capsules by scufiing pressures encountered in handling and storing the paper product, protective, particulate, buffer materials are commonly used in the capsule coat. Such materials are known as stilts in the trade. Stilts are commonly resilient materials, such as short-fiber alphacellulose, or hard, non-absorbent solid particles, such as minute glass beads. The less hard materials generally give a more satisfactory paper surface and allow the cap sules to be more readily and smoothly broken when it is intended to do so, but they also absorb, by capillary action,.quite an appreciable proportion of the expressed liquid when the capsule is ruptured and thereby prevent the etlicient transfer of the 'chromogenic liquid to the coreactant sheet. In commercial practice, both kinds of stilts are applied with absorbent binder materials, so that the use of known stilts is associated with a decrease in transfer efiiciency, as well as the desired decrease in accidental smudging. That is to say, the use of stilt materials always involves a compromise between frictional-smudge resistance and liquid-transfer efiiciency, the addition of absorbent stilt material and binders tending to increase the former and decrease the latter. The commercial papers in such record-unit systems show and depend upon a practical balance between these two properties. Any marked improvement in frictional smudge resistance without a loss in transfer etficiency constitutes a notable and useful advance in this art. The achievement of this improvement and advance is the object of this invention.

SUMMARY OF THE INVENTION The object of markedly increasing frictional smudge resistance without decreasing the transfer efiiciency of an encapsulated printing ink or dye in the presence of an absorbent stilt has now been realized by a new capsular unit construction based on a modification of the encapsulated aggregate or cluster of droplets disclosed in US. Pat. No. 3,041,289, which issued June 26, 1962, on the application of Bernard Katchen and Robert E. Miller. In pressure-sensitive record sheet manufacture, such an aggregated capsule unit is commonly provided with inner droplet material comprising a liquid solution of at least one colorless, chromogenic compound in a chlorinated biphenyl solvent. The new capsule unit structure, which gives improved transfer efficiency and smudge resistance, comprises a matrix of hydrophilic film material which bounds and retains liquid core materials as encapsulated aggregates of droplets wherein the droplets are of two kindsthe first kind being of about 0.5 to 2.5 microns diameter and being present in the capsule unit as one part by weight of the total liquid content and being a liquid solution of a colorless or colored chromogenic compound at four times the concentration of the solution ultimately to be released on rupture of the capsule, and the second, of about 3 to 5 microns diameter, being at least about 1 to 3 microns greater in diameter than the first kind of droplet, being present in the capsule as three parts by weight of the total liquid content, and being an inert, or non-marking, diluent liquid, such as the solvent used to make the solution in the first kind of droplet. In operation, the larger, inert-liquid-containing, capsules serve two functions. Prior to rupture, they protect the smaller, dyecontaining, capsules from accidental rupture due to indirect scuffing and handling pressures, and, at the moment of rupture, they release their contents, so as to dilute the released dye solution to the proper concentration and aid in its transfer to the second sheet, which is coated with color-developing co-reactant.

The concentration of the dye in the first kind of droplet and the relative weight-proportions of the two kinds of liquid droplets in the capsule may be varied at will. The concentration of the dye and the parts by weight to be used of the two kinds of droplets is chosen simply so that the delivered dye solution will be at the desired concentration after the capsules are ruptured and the different kinds of droplets are thereby mixed together.

The agent dispersed in the first kind of droplet need not be a dye but could be any agent dispersible in an organic oil whose chemical or physical properties are such that the agents retention and subsequent delivery would be useful. Medicines, perfumes, and other agents, whether solid or liquid, may be so encapsulated and protected from accidental rupture by incident pressures, but the system is particularly advantageous where such capsules are coated onto a supporting web where transfer efliciency to another surface or body is important.

3 DESCRIPTION OF THE DRAWING FIG. 1 shows diagrammatically a greatly magnified cross-section of a single capsule unit retaining aggregated and randomly-distributed droplets of different kinds and sizes suitable for use in this invention. The individual droplets are separated from each other by wall material which also forms a matrix for the whole aggregation to form a capsule wall of knobby conformation. The encased droplets, as shown, are of two kinds. One kind is a liquid dispersion of an agent such as a colorless, chromogenic dye compound dispersed in an organic solvent such as a chlorinated biphenyl. The other kind of droplet is an inert liquid which may be the solvent used in the first kind of droplet and is larger in diameter than the first kind, and forms larger protuberances, which protect the smaller droplets against indirect and unintentionally applied pressure. FIG. 1 shows each capsule as sectioned in a midplane, although in actuality a section through a walled cluster of capsules would show some in elevation in the background and others sectioned at various planes. Occasional rupture of a large protuberance releases only a harmless diluent.

FIG. 2 is a stylized edge-view of a portion of a paper coated with the capsule units of this invention. No attempt has been made to draw the different parts of the figure to scale, because the variation in size of eligible capsules and the variation in thickness of the possible supporting web materials useful in practicing the invention make relative dimensions impossible to be shown in a significant manner. Generally speaking, the thickness of the supportng web material, such as paper, is many times the average cross-sectional diameter of the capsule units individually. A coating of capsule units, one capsule unit in thickness, is ample, but more thickness can be tolerated.

DETAILED DESCRIPTION OF THE INVENTION In use as part of a paper-coating formulation to make a record unit, the minute capsule units of this invention, wherein the dispersed agent is a colorless, chromogenic dye, are coated onto paper from an aqueous suspension so as to give a random, even, distribution of capsule units, closely juxtaposed in interspersion on the paper surface. Such a sheet is called a CB (coated back) sheet, because it is commonly used capsule-coated-side down against an underlying sheet. The CB sheet may be used as the top sheet in a record unit couplet wherein the second sheet, known as a CF (coated front) sheet, has a coating which bears a co-reactant designed to react chemically with the released capsular contents of the CB sheet in contact therewith and produce a distinctively colored mark when and where the capsules are smashed by an intentionally applied pattern of marking pressures and the contents are expressed and transferred to the CF sheet. Such CB and CF sheets can also be used in multiple-sheet record unit forms as the top and bottom sheets, respectively. The intermediate sheets in such a multiple set usually are coated on both the front and the back to give what are known as CFB sheets. CFB sheets have capsular units bearing the chromogenic dye on the back coatings and color-developing co-reactant on the front coatings. The material and economic advantages of using the capsular units of this invention over the use of previously known capsules as the back coating in such CFB sheets are as pronounced as in the case of CB sheets in a couplet.

In the folowing table, test results are presented which show the effectiveness of the method and the materials of this invention when used in an eight-sheet multiplet. The tests are designed to compare the liquid dye transfer efficiency and frictional smudge resistance of two different types of CB and CFB sheets, one type prepared according to Example 2 of this invention and the second type being a standard CB or CFB sheet. The two types of sheets were coated from formulations identical in every respect except the actual capsule unit construction. That is, weights of stilt, binder, dye, and diluent per unit area of coated paper were as nearly identical as they could be made. Dye weights (in milligrams per square inch) were 0.073 for the Standard Sheet and 0.079 for the Test Sheet. The values given are Typewriter Intensity Index (TI) and Frictional Smudge Intensity Index (FS). These indices are ratios of reflectancesthe reflectances of the marks versus the papers background reflectance. Frictional smudge marks are measured in the same way as recording marks. A high index value indicates little color development, and a low index value indicates much color development. Thus a good record unit paper should have a low TI index value and a high FS index value.

Typewriter Intensity Index is defined by the following formula:

Printed Character Reflectance TIT Background Reflectance X100 Smudge Area Reflectance Background Reflectance where the smudge area coloration is produced by pulling a CF sheet over a CB sheet, coated sides together, with an eight-pound polished steel weight resting flat on the top of the CF sheet. The polished area of contact of the weight on the CF sheet is a circle 1.75 inches in diameter. The CF sheet and the weight are dragged by a steady pull on the CF sheet eight inches to the right, four inches up, and eight inches to the left over the CB surface. After a waiting period of ten minutes, the smudge area reflectance and the background reflectance are determined on the opacimeter.

FS: X100 NOTE: The better paper has the lower TI values and the higher FS values.

CB sheet: Sheet with coated back (chromogen-contaiulng capsules).

CF sheet: Sheet with coated iron (teidic ca-reactant receiving sheet).

TI-2: Typewriter Intensity of print on couplet receiving sheet. A value of 45 or less is considered commercially acceptable.

TI-618: Typewriter Intensity of print on sixth sheet down (a CFB sheet) 111 an eight-sheet multiplet. A value of 60 or less is commercially acceptable.

FS: Frictional Smudge Intensity. A value of or higher is commercially acceptable where 100 signifies no smudge. All OF sheets were coated as laboratory preparations with a coating weight oi five pounds per ream of 3,300 square feet.

Test sheet: 013 sheet of Example 2 or CFB sheet with the CB coat of that example, prepared in a pilot plant operation.

Standard; CB sheet, prepared in a pilot plant operatiou according to a commercial formulation-encapsulated aggre ates of dyesolution droplets of uniform size plus short-fiber alpha-cc lulose stilt plus starch binder material.

Consideration of the FS values in the table reveals a marked increase in frictional smudge resistance of the novel coated paper (CB sheet) of Example 2. The average FS value for the Standard CB sheet of commercial formulation is 84, while that of the test sheet is an improvement of 13% in a formulation that is already commercially acceptable and that is already performing near the top of the possible range. The Typewriter Intensity Indices show good ink transfer efliciency in all cases. It is noteworthy that the TI values for the Test Sheet of this invention are also generally improved alllld never significantly worse than those of the Standard S eet.

The performance of the capsule units in resisting the release of dye material retained in the small droplets when subjected to moderate frictional or non-smashing pressures and releasing properly diluted dye material with good transfer efficiency when subjected to marking pressures sufficient to smash the entire capsule unit and resulting in dilution of the concentrated contents of the small droplets is in accord with the concept of design that guided the construction of the capsule units. Photomicrographs show the capsule units to be as described and pictured herein. The larger droplets do indeed protrude from the aggregate and cause larger bulges in the exterior surface of the polymeric film matrix material, so that the dye-bearing smaller droplets are protected from shock and release due to handling pressures of non-marking value. The larger droplets are believed to protect the smaller droplets both because of the geometry of the construction of the capsule unit and because of the larger droplets absorption and dissipation of energy brought to bear by sudden applied pressure changes of undefined vector pattern and of less than smashing force.

The following specific examples show the preferred and other embodiments of the invention and are not intended to limit the scope of the utility of the invention disclosed.

Aggregations of droplets, encapsulated and retained separately in the polymeric matrix of film material, result from the preparative procedure of Example 1. Aggregation of the emulsified droplets is believed to occur early in the coacervative deposition process as soon as the surface characteristics of the mutually repellant droplets of the emulsion have been modified by the deposition of somepolymeric film material, which is the first deposited part of the emergent or coacervate phase of the process.

Once the mutual repulsion of the droplets is destroyed by the emergent film material, aggregation occurs, and further deposition of the emergent phase covers the whole aggregate with polymeric film wall material to give the multiple-droplet capsule unit.

The dye component for use in making marks by color reaction may be of the colorless, chromogenic kind, such as crystal violet lactone alone or mixed with benzoyl leuco methylene blue, as in Example 1, or any of many colorless chromogenic materials known in the art, many of which are noted in an application for United States letters Patent, Ser. No. 392,404, filed Aug. 27, 1964, by Robert E. Millerand Paul S. Phillips, Jr., now abandoned, but'the substance of which is published in British Pat. No. 1,053,935 (1966), corresponding thereto, and which is disclosed in continuation United States patent application Ser. No. 744,601, filed June 17, 1968. The dye could also be already colored to form a printing ink solution or dispersion, such as a dispersion of carbon black in an organic oil, such a system not requiring a sensitized transfer receiving sheet.

The novel system could be used with any aggregated droplet system for use in making a coated unit of one or more sheets such as film or fabric such as paper. However, the main advantage of this invention will be found in units of two or more sheets of the kind where liquid ink or marking liquid is transferred from one sheet to another, since the peculiar advance represented by this invention is protection against frictional smudging without loss of transfer efficiency by the architecture of the system.

Dispersion as used in this disclosure does not exclude solutions which are viewed herein as extremely fine dispersions or molecular dispersions.

The solvent used to dissolve or disperse the chemical agent or dye and the inert, or non-marking, liquid of the larger droplets may be the same or different and may be readily and appropriately chosen from among nonviscous, water-insoluble, organic liquids.

The material used as the retaining matrix for the droplets is preferably gelatin-gum arabic complex, as shown in Example 1, but any hydrophilic, polymeric, film-forming material suitable for use in making aggregated capsule units would be within the scope of this invention.

6 EXAMPLE 1 Preparation of encapsulated aggregate of droplets Two aqueous emulsions were prepared separately, one having dye-containing oil droplets of about 2 microns diameter and the other having oil droplets (without dye) of about 4.5 microns diameter. Both emulsions were prepared by stirring the compositions in a Waring Blendor at 55 degrees centigrade until the desired droplet dimensions were obtained. Approximate, average droplet diameters Were determined by use of optical transmission data obtained on the emulsions or by direct, microscopic observation through a reticle of small samples of the emulsions removed from the stirred mixture. The gelatin used was as an aqueous solution of pigskin gelatin with an iso-elcctric point at about pH 9 made up as an 11% by weight concentration at a pH of 6.5. The formulation of the two emulsions was:

Deionized water 18 56 The oil phase of Emulsion 2 was a 221 Weight mixture of Aroclor 1242 and Magnaflux oil, the first oil being a chlorinated biphenyl supplied by Monsanto Chemical Company, St. Louis, Mo., United States of America, and the second oil being a hydrocarbon oil with a distillation range of 370 to 500 degrees Fahrenheit, supplied by Magnaflux Corporation, Chicago, 111., United States of America. The oil phase of Emulsion 1 was the same as for Emulsion 2, except that it had dissolved in it 6%, by weight, crystal violet lactone and 5%, by weight, benzoyl leuco methylene blue, the colorless chro mogenic dyes to be used herein as mark-formers.

The two emulsions were combined in a beaker with continual stirring, and the pH of the resultant mixed emulsion was adjusted to 9 with a 20%, by weight, aqueous sodium hydroxide solution. To the stirred emulsion were then added 11 grams of 5%, by weight, aqueous solution (pH adjusted to 8 with 20% sodium hydroxide) of poly(methyl vinyl ether-maleic anhydride) copolymer such as a Gantrez AN copolymer with a specific viscosity (1 gram of copolymer in milliliters of butanone and determined at 25 degrees centigrade) of 0.9 to 1.0 poise as supplied by General Aniline and Film Corporation, New York, N.Y., United States of America, 91 grams of an 11%, by weight, aqueous solution of gum arabic, and 655 grams of hot (approximately 65 degrees centigrade) deionized water. At this point, the temperature of the mixture was adjusted to 55 degrees centigrade, and the pH was again adjusted to 91. Then, with the mixture under continuous agitation, the following steps were taken: (1) 13.5 mililiters of 14%, by weight, aqueous acetic acid was added dropwise, (2) the mixture was cooled to 12 degrees centigrade and treated with 7.5 milliliters of 25%, by weight, aqueous glutaraldehyde, (3) one hour later, 15 milliliters of a 5%, by weight, aqueous solution of poly(methyl vinyl ether-maleic anhydride) copolymer (at pH 8) was added dropwise, and finally (4) one-half hour after the preceding addition was complete, the pH was raised to 10 with 20% sodium hydroxide solution.

The now-completed capsule units thus prepared may be isolated from the vehicle by decantat ion, centrifugation, or filtration, washed, and dried, or more conveniently used without isolation as a suspension in the aqueous manufacturing vehicle.

EXAMPLE 2 CB Paper-The aqueous suspension of capsule units prepared in Example 1 was used without recovery of the capsule units from the manufacturing vehicle. The CB coating was prepared according to the following formulation:

Dry weight, Solids, Wet weight, grams percent grams 2 000 10, 000 Alpha-cellulose 1 400 100 400 Tale (powdered) 200 100 200 Starch (aqueous) 9 200 20 1,000 Win for 2, 400

The coating slurry was applied to paper with an air knife coater to give a coating weight of 4.2 to 4.5 pounds per ream of 3,300 square feet after the paper was ovendried at 200 degrees Fahrenheit.

EXAMPLE 3 Encapsulated aggregates were prepared according to the procedure of Example 1 except that the liquid portion of the oil phase of Emulsion 1 and Emulsion 2 was entirely Aroclor 1242.

EXAMPLE 4 Encapsulated aggregates were prepared according to the procedure of Example 1 except that the liquid portion of the oil phase of Emulsion 1 and Emulsion 2 was entirely tetrachloroethylene.

What is claimed is:

1. A pressure-sensitive record unit comprising a sheet of paper supporting as a coating on one of its surfaces a closely-spaced layer of capsule units wherein substantially all of the individual capsule units consist of large and small droplets of liquid randomly distributed in a cluster of droplets and protectively retained individually and collectively in a pressure-rupturable matrix of solid polymeric film material, the matrix conforming to the cluster shape and exhibiting large bulges where covering large droplets, the large droplets being on the average at least about one to three microns greater in diameter than the small droplets and consisting of about three parts by weight of non-marking diluent and the small droplets being about one part by weight of a concentrated liquid solution of marking material, whereby non-smashing pressures applied to the unit tend to break the polymeric material only at large-bulged places to release the associated large droplets from the matrix and whereby smashing pressures applied to a unit by a marking device release a diluted free-flowing quantity of marking fluid comprising a mixture of the contents of the large and small drop lets.

2. A method of providing a paper record sheet with minute liquid droplets of marking material easily released locally by applied marking pressures but resistant to release of appreciable marking amounts by applied pressures of handling, creasing, and bumping, consisting of the steps of providing two miscible liquids, a first one being about three parts by weight of a diluent with no marking propensity and the second one being about one part by weight of a concentrated solution of a marking material; dispersing the two liquids separately in solutions of liquid film-forming polymeric material to make two emulsions of minute droplets, the emulsion of the first liquid having droplets of at least about one to three microns larger diameter than the emulsion of the second liquid; combining the two emulsions so as to give a random mixture of the two kinds of liquid droplets; depositing by coacervation and hardening a polymeric film about each of the droplets individually and about the exterior of aggregates of the droplets, said aggregates spontaneously [forming during the coacervation so as to give a capsule unit consiting of the two kinds of droplets and the polymeric film material which forms a matrix to retain the two kinds of droplets, the larger droplets of nonmarking diluent causing protuberances in the deposited retaining film of the capsule unit and being released by pressure more readily than the smaller droplets of marking material; applying an aqueous suspension of the cap sule units to a paper surface in an amount to closely cover the surface; and drying the paper so as to leave a coat of the capsule units on the paper surface.

References Cited UNITED STATES PATENTS 3,617,334 11/1971 Brockett et al. 117--36.2 3,041,289 6/1962 Katchen et al. 117-36.2 3,481,759 12/ 1969 Ostlie 117--36.2 3,016,308 1/1962 Macaulay 117--36.7 3,179,600 4/1961 Brockett 117-36.2 2,655,453 10/ 1953 Sandberg 1'1736.1 2,711,375 6/1955 Sandberg 117-36.1

MURRAY KATZ, Primary Examiner US. Cl. X.R. 

